1. Field
The present invention relates generally to wireless power transfer, and more specifically to devices, systems, and methods related to wireless power transfer to remote systems such as vehicles including batteries.
2. Background
Approaches are being developed that use over-the-air or wireless power transmission between a transmitter and a receiver coupled to the electronic device to be charged. Such approaches generally fall into two categories. One is based on the coupling of plane wave radiation (also called far-field radiation) between a transmit antenna and a receive antenna on the device to be charged. The receive antenna collects and rectifies the radiated power for charging the battery. This approach suffers from the fact that the power coupling falls off quickly with distance between the antennas, so charging over reasonable distances (e.g., less than 1 to 2 meters) becomes difficult. Additionally, since the transmitting system radiates plane waves, unintentional radiation can interfere with other systems if not properly controlled through filtering.
Other approaches to wireless energy transmission techniques are based on inductive coupling between a transmit antenna embedded, for example, in a “charging” mat or surface and a receive antenna (plus a rectifying circuit) embedded in the electronic device to be charged. This approach has the disadvantage that the spacing between transmit and receive antennas must be very close (e.g., within millimeters). Though this approach does have the capability to simultaneously charge multiple devices in the same area, this area is typically very small and requires the user to accurately locate the devices to a specific area.
Recently, remote systems such as vehicles have been introduced that include locomotion power from electricity and batteries to provide that electricity. Hybrid electric vehicles include on-board chargers that use power from vehicle braking and traditional motors to charge the vehicles. Vehicles that are solely electric must receive the electricity for charging the batteries from other sources. These electric vehicles are conventionally proposed to be charged through some type of wired alternating current (AC) such as household or commercial AC supply sources.
Efficiency is of importance in a wireless power transfer system due to the losses occurring in the course of wireless transmission of power. Since wireless power transmission is often less efficient than wired transfer, efficiency is of an even greater concern in a wireless power transfer environment. As a result, there is a need for methods and apparatuses that provide wireless power to electric vehicles.
A wireless charging system for electric vehicles may require transmit and receive antennas to be aligned within a certain degree. Differences in distance and alignment of transmit and receive antennas impacts efficient transmission. Therefore, a need exists for adapting link parameters in a wireless power transfer system in order to improve power transfer, efficiency, and regulatory compliance.